1. Field of the Invention
The present invention relates to a field effect transistor (referred to as FET hereinafter) and more particularly to a FET suited to be made in integrated circuit form. Further it relates to a high frequency signal oscillator containing the FET as active element, and a frequency converter containing the oscillator.
2. Description of the Prior Art
The frequency converter of a high frequency (RF) receiver which receives electric waves of SHF band direct satellite broadcasting (DSB) from a geostationary satellite produces an intermediate frequency signal in response to a local oscillation signal from a local oscillator and the above-mentioned SHF band signal. The local oscillator is usually provided with a gallium arsenide field effect transistor (referred to as an GaAs FET, hereinafter) as active element, and the frequency of the local oscillation signal is stabilized by an dielectric resonator. The local oscillator and the frequency converter are desired, for the sake of scale-down or economy to be made in hybrid or monolithic integrated circuit form.
Many of this type conventional local oscillators used are reflection type oscillators. An example of them is described in the following literature: Shinkawa et al., "SHF Converter formed on A Single Teflon-Fiberglass Substrate for Satellite TV Broadcasting", Institute of Television Engineers of Japan, Technical Report (RE83-40) pp. 7-11, Oct. 27, 1983. Disclosed in that citation is a drain-grounded oscillator including as an active element, a GaAs FET the drain terminal of which is grounded for high frequency. The gate terminal is connected through a coupling line to a dielectric resonator, and the source terminal is connected to a capacitive reactance and a load. The capacitive reactance with a suitable value produces a negative resistance at the gate terminal. When the line impedance of the coupling line and the distance between the gate terminal and the dielectric resonator, respectively, are properly set, a high frequency signal is produced and outputs from the source terminal.
The following requirements are imposed to the reflection type oscillator: to create a great negative resistance at the source terminal of the GaAs FET and to be placed in impedance-matching with the load. It is very difficult to fulfill the above-mentioned two conditions by only the adjustment of the capacitive reactance connected to the source terminal. In other words, if, because of great variation of the negative resistance appearing at the gate terminal with the capacitive reactance added to the source terminal, the value of the capacitive reactance is set to meet the oscillation conditions at the gate terminal, it would be impossible to match with the load so as to obtain the maximum oscillation signal output at the source terminal.